1. Field of the Invention
The present invention relates to a vibration wave driven apparatus and, more particularly, to a vibration wave driven motor of the type in which an elastic member in which a traveling wave is generated is held in pressure contact with a rail-type stator so that the elastic member is moved along the rail-type stator.
2. Description of the Related Art
FIGS. 6 and 7 show one of known vibration wave driven motors. Referring to these Figures, the vibration wave driven motor has an elongated circular elastic member 1 provided with a projection 1a on its sliding side. A piezoelectric element 2 for generating a traveling vibration wave is joined to the upper side of the elastic member 1. Numeral 8 denotes a rail-type stator which makes frictional contact with the elastic member 1. The elastic member 1 is held in pressure contact with the stator 8 as the elastic member 1 is urged by a pressing spring 3 through an insulating member 5 such as, for example, a felt layer. Numeral 6 denotes a comb-like stopper with teeth 6a thereof received in slits formed in the portion of the elastic member 1 which is not in contact with the rail-type stator 8, so that the elastic member 1 is supported by the teeth 6a through pieces 7 of felt provided in the bottoms of the slits.
The elastic member 1 is carried by a table 4 through the stopper 6, pressurizing spring 3 and so forth. The table 4 is supported by a restriction member 9 which restricts the movement such that the table 4 is movable only in predetermined directions B.sub.Y.
When a traveling vibration wave is generated in the elastic member 1 of the described apparatus, the elastic member 1 moves along the rail-type stator 8 so that the table 4 and other members 3, 5, 6 and 7 also move in the direction of the arrow By along the restriction member 9. Meanwhile, the generated frictional drive force acts on a portion of the elastic member 1 which is offset from the supported portion of the elastic member 1, a moment is generated to act on the elastic member 1 to undesirably cause a movement of the elastic member 1 in the directions of arrows B.sub.X and B.sub.Y.
As will be seen from FIG. 7, the teeth 6a of the stopper 6 are received in the slits formed in the elastic member 1 so as to restrict the displacement of the elastic member 1 in the direction of the arrow By and to bear the weight of the elastic member 1 through the pieces 7 of felt. The stopper 6 also has restricting portions 6b and 6c which restrict the displacement of the elastic member 1 in the direction of the arrow B.sub.X, and a restricting portion 6d which restricts the movement of the pressed portion of the elastic member 1 in the direction of the arrow By.
The elastic member 1 and/or the stator 8 is inevitably deformed due to,for example, a change in temperature. It is therefore extremely difficult to keep a face-to-face contact between the elastic member 1 and the rail-type contact member 8. Actually, therefore, the elastic member 1 contacts with the stator 8 in a slightly inclined state as shown in FIG. 8 or FIG. 9. More specifically, in the state shown in FIG. 8, the elastic member 1 makes a line contact with the rail-type stator 8 at its edge 1b which is often rough due to presence of a burr. On the other hand, in the state shown in FIG. 9, an edge 8a of the rail-type stator 8, which also is rough, makes a line contact with the elastic member 1. In the known vibration wave driven apparatus, therefore, it has been difficult to attain a smooth and stable movement of the elastic member 1 and to obtain a high degree of durability.